1. Field of the Invention
The present invention relates to an apparatus for digitally recording and/or reproducing data into and/or from a disc-shaped recording medium such as a magnetic disc, optical disc or the like, and a disc-shaped recording medium usable in the apparatus and into and/or from which data is recorded and/or reproduced.
2. Description of Related Art
Conventionally, to record information into a magnetic disc, a magnetic head is moved radially of a magnetic disc based on positioning information to move a magnetic head to a predetermined position, which is being reproduced.
The head positioning information is usually called "tracking servo signal" and composed of a so-called track address indicative of a data track number, and a fine signal indicative of a fine position in the data track. Generally, the tracking servo signal is recorded on a magnetic disc beforehand by means of a device called "servo writer".
The tracking servo signal is recorded in zones defined by segmenting a magnetic disc circumferentially. Of such zones, a one where a tracking servo signal is recorded will be referred to as "servo zone" herebelow, and a zone where no tracking servo signal is recorded, namely, where data is recorded, will be referred to as "data zone" herebelow. Such a common disc format is illustrated by way of example in FIG. 1. In the illustrated example in FIG. 1, the servo zones count twelve in number but an actual disc consists of tens to hundreds of servo zones.
The configuration of a common servo zone is illustrated in detail by way of example in FIG. 2.
In the example illustrated in FIG. 2, the servo zone consists of a track address indicative of a data track No., a fine signal indicative in detail of a position in the data track, and a clock mark located between the track address and fine signal to extract a sync clock necessary for reproduction of these signals. All these signals are recorded in a format which is already disclosed, for example, in the U.S. patent application Ser. No. 08/588,020 of the Applicant of this patent application.
FIG. 3 illustrates the configuration of a general tracking servo system of a magnetic disc drive, showing major components of the system. It should be noted that another tracking servo system is not illustrated in FIG. 3.
As seen from FIG. 3, a magnetic head 9 reproduces a signal from a magnetic disc 11. The reproduced signal is amplified by a reproduction amplifier 15, and then converted to a digital signal by an A/D (analog/digital) converter 16. For acquisition of tracking servo signals, the digital signal is passed to a track No. detector 17 and a fine signal detector 19. From the digital signal, the track No. detector 17 detects a track No. while the fine signal detector 19 detects a fine signal. Thus, the track No. signal and fine signal are extracted as tracking servo signals. When reproduced, the fine signal shows a value of 0 when the magnetic head 9 is positioned in the center of a data track, for example, and a value of .+-.0.5 when the magnetic head 9 is positioned .+-.1/2 of one track pitch off the center of the data track.
A current position calculator 18 is provided to calculate from the detected tracking servo signal a radial position where the magnetic head 9 exists, and a value indicative of the radial position is passed to a positional difference calculator 8 which is also supplied with a value of a target position. In this positional difference calculator 8, a difference between the radial and target positions is determined.
Also a positioning compensator 14 is provided to generate a VCM (Voice Coil Motor) control signal for the difference between the radial and target positions to be zero. The VCM control signal is converted to an analog signal by a D/A (digital/analog) converter 13, and then passed to a VCM driver 12 which drives a VCM (voice coil motor) 10. The voice coil motor (VCM) 10 moves the magnetic head 9 radially over the magnetic disc 11.
It should be appreciated that for continuous recording and reproduction of large amount of data, a faster access is possible to a spiral data track rather than to a concentric data track. It is assumed here that a greater amount of data than recordable on one track for one round of a magnetic disc is to be recorded on the magnetic disc. If the magnetic disc has data tracks formed concentrically thereon, data for one data track is first recorded, and then the magnetic head is moved to a next data track for recording the rest of the data. On the contrary, if the magnetic disc has a data track formed spirally thereon, data can be continuously recorded on the track without the necessity of moving the magnetic head from one track to another as in the magnetic disc having the concentric data tracks.
Also in a magnetic disc having concentric data tracks, a time required for the magnetic head to move from one to a next of the concentric data tracks formed on the magnetic disc varies and it is difficult to assure that the magnetic head can be moved from one to another track within a predetermined time. Therefore, a magnetic disc having such concentric data tracks is not so much suitable for recording and reproducing an information which should be real-time or continuously recorded or reproduced, such as image information, for example. A magnetic disc having a data track formed spirally thereon is suitably usable for such a purpose.
Usually, however, a tracking servo signal is recorded concentrically on a magnetic disc, and it is extremely difficult to record the signal spirally on a magnetic disc. For recording or reproducing data with respect to a magnetic disc having concentric data tracks formed thereon, it suffices to move the magnetic head a half track pitch when positioning information is recorded concentrically on the magnetic disc by means of a servo writer. For spiral recording of the positioning information, however, it is necessary to move the magnetic head over tens to over hundreds of one track pitch. It is very difficult to attain such a high accuracy in moving the magnetic head over the magnetic disc.
Conventionally, data recording and/or reproduction into and/or from a magnetic disc is thus made with respect to the concentric data tracks formed on the magnetic disc.